Cathode-ray tube control circuit



Nov. 1 194 v E. .1. lSBlSTER ETAL 2,453,711

CATHODE-RAY TUBE CONTROL CIRCUIT Original Filed July 30, 1942 1 9 4 3.9 4.? 4A 2 CONTROL 501171;;5 PULSE 05671147012 FHA 65 657153470 GENERATOR S/IIFTER E L- v 3 SQUARE 5 6 WA v1: 7 1 v 7 msnmm ENERATDR RECEIVER |NVENTOR g .ER/c d. Ass/$717? WALTER D N A o'RNE Patented Nov. 16, 1948 Eric J. llsbister, Forest Hills, and Walter N. Dean,

LarchmonaN. Y., assignors to The Sperry Cor- Original application Divided and Serial No. 504,872'

poratiorga corporation of Delaware July 30, 1942, Serial No.

this application October 8 Claims (01. 315- 22) This invention relatesto control circuits for cathode ray tubes which are particularly useful in radio detection systems such as that disclosed in copending application Serial No. 452,818, filed July30, 1942, in the names of Eric J. Isbister et al., of which the present application is a divi- SlOIl. r

In such radio detection systems, the distance to a distant object may be determined by radiating a recurring sequence of pulses of high frequency radiant energy toward the target, receiving the" pulses reflected therefrom, and positioning a member in accordance with the time'- phase positicn of the received pulses relative to the transmittedpulses. According to the present invention, improved apparatus is provided for indicating correspondence between the positioning of'thi's range-indicating or range-tracking member with the time-phase just referred to. The improved range indication which indicates this correspondence is obtained by producing a wave shape on the screen of the cathode ray tube Corresponding to the envelope of the entire received wave, and bymagnifying' the" time scale of that portion of the indication l corresponding to the time-phase position of the range indicating member. Further improved circuit means are providedfor' intensifying the indication of this magnified portion relative to the remainder of the trace, to provide a clearerand more useful type-or indication. i

" The magnification of the time scale of a selected portion of the indicationis'accomplished by acontrol circuit -for a cathode ray tube which periodically sweeps the electron beam across the screen of the tube and accelerates the beam during a selected portion of the sweep. In this manner, the indication on the screen is expanded or magnified for a predetermined interval the time phase ofwhich ismanually adjustable.

In orderto maintain the intensity of the trace or indication during the accelerated period of the sweep, the intensity of the electron beam and the trace is controlled according to the instantaneous velocity of the beam. This is effected by difierentiatingthe sweep voltage and applying the differentiated voltage to the intensity controlgrid of the cathode ray tube.

It is a major object of this invention to provide a control circuit'for a cathode ray tube in which the rate of change of a varying sweep voltage may bevaried for a predetermined interval. 1

A further object ofthe invention isto provide a range indicator for a pulse; detectionsystem and to attract attention in which the time-phase of a magnified portion of the trace indication is adjusted to correspond to the time-phase of a received pulse.

A further object of the present invention is to provide an improved electronic indicator for indicating'the time-phase position or acontrol member relative to a periodic wave in such manner as to render the indication extremely clear thereto and focus interest thereon by magnifying a selected portion of theindication. l

A still further object of the present invention is to provide improved circuit means for controlling the intensity of the trace of a cathode ray'tube havinga non-linear sweep voltage producing a non-linear sweeping of the cathode ray beam, wherebythe eiiect of varying velocity of the electron. beam upon the trace is substantially eliminated by the control of the intensity of the beam in accordance with this velocity, and the brightness of the tracemay even be increased. Further objects and advantages will become apparent from the following specification and accompanying drawings, wherein :Fig. .1 is a schematic diagram of a control circuitfor a cathode ray tube embodying the invention;

Fig; 2 .shows a series of voltage versus time curves useful in explaining the operation of the circuits; and a Fig.3 shows a representation of the cathode ray tube screen during normal operations.

Referring first to Fig. 1, there is provided a control oscillator I of any conventional type adapted tofpro'duce an alternating control voltage of suitable frequency, preferably in the audio frequency range as represented by the sine wave 2 in Fig. 2A. Suitable values of this control frequency havelbeen found to lie between 400 and 2,000 cycles per second. The output of control oscillator l is fed to a square wave generator 3.,of any conventional type adapted to produce in its output asubstantially square wave having a frequency corresponding to that of the control oscillator l. The output of square wave generator 2cmay be led, as by a conductor 5, to a high frequency transmitter 6 which radiates periodic pulses of. high frequency energy of short duration and suitable amplitude, and having a repetitionrate corresponding to the frequency ofthe square wave generator 3 and of the control oscillator l.

The envelope of the wave radiated by transmitter 6 willthen consist of a plurality of short pulses having .a'. time phasexand. repetition rate determined by the voltage output wave 2 of the control oscillator I. Since these pulses will take a finite time to travel to the reflecting object and back to a receiver 9, the received wave will contain corresponding pulses which are delayed in time phase with respect to the transmitted pulses by an interval 16 proportional to the distance to the distant object.

in order to determine the range of the object from which received pulses are reflected, it is necessary to determme the time interval t by may be determined by measuring the time-phase displacement between transmitted and received pulses. For this purpose, the entire received wave from receiver 9 is impressed'upon vertical deflecting plates II and I2 of cathode rayindicating tube I3 so pulses corresponding to detected objects appear on the screen of the tube.

Horizontal deflection of the cathode ray beam is-,controlled by a sweep circuit having, an accelerated portion which maybe adjusted to cincide with a selected one of -the received pulses. By calibrating the time phase of the adjusting member, it is possible to determine range of an. object according to the time phase of pulses reflected therefrom with respect to transmitted pulses. .JIheelectron beam is swept horizontally synchronously with the transmission of pulses of high frequency energy by a circuit that is controlled by the square wave generator 3.

A sweep-square wave I6. (Fig. 2D) obtained from square wave generator 3 by means of lead ii is impressed byway of asuitable coupling condenser I8 and grid resistor I9 upon the control grid; 2I of a sweep control tube 22, whose anode '23 is connected directly to a source of positive potential such as 24, and whose cathode, 2-5 is connected'to the anode 26 of expander control tube 21, whose cathode 28 is connected to ground through a suitable biasing resistor 29. This. sweep square. waveHi has a predetermined fixed phase relation with respectto the pulses radiated by the transmitter .6 since these radiated pulses are also derived from the square wave generator 3; Preferably, although not necessarily, the radiated pulses are initiated at the same instant as the square wave pulses I6 terminate.

Selectively connected between anode 26 of tube 27 and ground, as by means of a switch 3I, are condensers 32, 33 having differing capacitances, applying as will be seen,.diiferentrates of sweep to horizontal deflecting plates 34' and 35 of the cathode raytube i3. Assuming for the moment that condenser 32 is thus connected in the circuit by means of switch 3 I, it will be clear that during the positive half cycles of the sweep square wave I6, when tube 22 is conductive, condenser 32 will be charged to a voltage corresponding to the amplitudeof the sweep square wave I6. The amplitude of the sweep square wave I6 and the value of resistor I9 are so-chosen that during the negative half cyclesof the sweep square wave I6, control tube.22 is completely blocked. Accordingly, condenser 32 will then discharge through tube 2?, providing a voltage to horizontal deflecting plates 34 and 35 of the type shown at '37 in The discharging voltage of condenser: 32, corresponding to the portion 38 of wave 37, willvary substantially linearly with time, since pentode tube 21 is essentially a constant currentdevice, as is wellknow'n- Hence this voltage may be used as a time sweep'voltage for range However, this provides no inindicator tube. '13.

delayed. This time interval of normal size.

4 dication of the relative phase position of the range pulses, as is desired.

In order to provide such an indication, the rate of change of this sweep voltage 38 is momentarily greatly increased at a selected time phase position.

The control voltage 2 derived from control oscillator I is conducted to an adjustable phase shifter 39 of any conventional type, whose phase shift is adapted to be controlled by manual control knob 4|. The output of phase shifter 39 thus comprises a sine voltage wave adjustable in timephase as shown at 42 in Fig. 2B. This voltage wave is supplied to a suitable square Wave generator 43 and thence to a pulse generator 44 to produce pulses 4'! as shown in Fig. 20. It will be clear that, by suitable adjustment of phase shifter 39, the phase of the square wave output of generator 43 and of the pulses of generator 44 may be suitably adjusted with respect to that of control oscillator I as desired, The duration of these generated pulses 41 is preferably substantially equal to that of longer. These generated range pulses 47 from range pulse generator 44 are fed to control grid 48 of expander control tube 27 whose anode-cathode circuit is connected in shunt with condenser 32. During the interval between the range pulses 4! tube 2'! exhibits a high resistance which determines the discharge rate of condenser 32 as repnormal high'resistance, and the discharge of con.. denser 32 then returns substantially to its original rate for the remainder of the sweep as shown at 52in Fig. 2F.

Accordingly, the cathode ray relatively slowly val SI, creased, thereby eiTectiVely magnifying the time scale for this portion of the sweep. For the remaining portion 52 of the sweep the slow rate is resumed.

Hence, as shown in Fig. 3, during the intervals 49 and 52, the image of the receivedwave will be During interval 5|, however, this image will be greatly widened. By making this widening efiect of a marked character, a distinct indication is produced of the time phase position of the generated pulse 41 relative to the received wave.

Accordingly, the operator, to determine the range of an object, operates manual control M to maintain the image 55' (Fig. 3) of a selected received pulse in a magnified condition on the screen of indicator I 3, while any other pulses 56, or noise waves will only have unexpanded appearance. In effect, by proper choice of the rate of change of the sweep voltage during intervals 49 and 52' relative to that during interval 5|, pulses 56 of Fig. 3 may be made to have the character merely of short vertical line segments, whereas the actual wave shape of the desired received pulse 55-may be made much clearer by its magnification during interval 5|.

The speeding up of the sweep of the'electron beam in range indicator I3 causes a definite decrease in brightness of the trace'produced thereby during this expanded portion. .In order to avoid the transmitted pulses or slightly the sum of the wave forms this. effect and if. desired-,tomake. the brightness of the .expandedportionof the trace greater. than that of'the remaining portionof theindication, an intensifier circuit isused to control the-brightnessof thetrace, v i

Forthis purposethe sweep. voltage .applied to the horizontal-deflecting plates, 34 and 35 1s also connected .by-lead 59) to a differentiating circuit comprising condenser'fil and resistor 62. As is well known, the voltage across resistor 62, if its resistance is of a low value compared'to the reactance ofcondensertl at thefrequency of the principalcomponents of the input wave, will be substantially a pure time derivative of the voltage on lead1 59..HThis voltage across resistor 62 is shownin Fig. 2G, having a constant low magnitude;;during intervals 64 and65 corresponding to the low rates ofchange ,during the portions 49 and 52 -of the sweep voltage, and having a highvalue 66 during the highrate of change portion filjof-the sweep voltage,

Since the brightness of thetrace is substantially inversely proportionalto the velocity of the trace and substantially directly proportionalto the voltage applied to; intensity control grid 61 of; indicator. IE, it will be seen that by impressing the voltage wave of Fig. 2G upon intensity controlgrid 61 the resulting trace will have substantiallyconstant brightness during the entire sweep. Also the electron beam will be effectively cut off during the periods inwhich the sweep voltage does not occur,;as is very desirable in order to prevent stray indications which might confuse the operator; ,j w

However, it is preferable that the brightness of the expanded portion of the trace be further increased in order to provide more easily visible indication of the desiredtracking condition. For this purpose it is necessary to increase the magnitude of the high amplitude portion 66 of the intensifier voltage of Fig. 2G.

The diilerential voltage across resistor 62 is applied through an, amplifierlfl to control grid 'H oftube 13, whose anode'lz is connected to a source oi'high positive potential 14 and whose cathode, isconnectedto ground through aresistor 16. a 1,A further tube 11 is provided in parallel with tube 13 and having its control grid 18 energized from the pulse generator 44 by way of lead 19, couplingacondenser 80, and. grid input resistor 8|. Cathode 82 of the tube 11 is connected to common cathode bias resistor 16. Anode 83 of the tube Tlr'nay be connected to the positive source 14.

has been described above, and as is shown in Fig. 2G, the time phase position of the high amplitude portion 66 of the intensifier voltage is the same as the time phase position of the generated pulse '41; since tubes 73 and 11 are actuated by voltages as shown in Figs. 2G and 20 respectively, the cur-rents through those tubes correspond to those waves. These currents are added in common cathode resistor 16 and, accordingly, the voltage appearing across the resistor 16 will have a wave form corresponding to of Figs. 2G and 2C. In other words, it will have the wave form shown in Fig. 2H, in which the large amplitude portion 85 now has a magnitude which is increased relative to the magnitude of the low intensity portion 86.

This wave of Fig. 2H is then applied to the intensity control grid 61 of indicator l3 by way of lead 88 to produce the desired increased brightness of: the expanded indication $5 shown in Fig. 3.

Since, as described above, the time phase ofthe reflected pulse relative to the radiated pulse is a measure of the distance or range of the reflecting object, it will be seen that the phase shift required to synchronize the generated pulses 41 with the reflected received pulses corresponds to the range of the object. Accordingly, the setting of manual control 41 may be used to indicate this range directly, by the use of a suitable scale 9| associated with the control 4!. i.

From the foregoing description of the control circuit for the cathode ray tube it will be apparent that the velocity of the sweep of the electron beam may be varied during any desired portion of the sweep. The beam may be accelerated during an interval having an adjustable time phase relative to the normal sweep. By adjusting the time phase of the accelerated interval to coincide with the reception of a reflected pulse, it is possible to determine the range of an object from which energy is reflected since the normal sweep and the acceleration interval, as well as the transmitted pulses, are synchronized by the same control oscillator.

, Since the intensity of the indication trace would normally decrease when the sweep is accelerated, the intensity control grid of the tube is controlled according to the velocity of the electron beam so the intensity of the trace is substantiallyyconstant. If desired, the trace can be made brighter during the accelerated period by actuating the intensity control grid by the same signal as that which controls the acceleration of the sweep. I Although the cathode ray tube control circuit described herein is applied to a radio range finder in-an object detection system, it is not intended that it should be limited to such use. Obviously any source of signal to be observed might be substituted for the receiver 9, or the receiver might be used to detect signals other than those reflected by an object.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A control circuit for a cathode ray tube having beam deflecting electrodes and a beam intensity control grid, comprising means for applying a varying sweep voltage of predetermined direction to said electrodes, means for changing the rate of variation but not the direction of said sweep voltage for. a predetermined interval, and means actuated by said last-named means for controlling said grid to alter the brightness of the beam trace during said interval.

2. A control circuit for a cathode ray tube having beam deflecting electrodes and a beam intensity control grid, comprising means for applying a varying sweep voltage of predetermined direction to said electrodes, means for changing the rate of variation but not the direction of said sweep voltage for a predetermined interval, means actuated by said sweep voltage for controlling said grid to maintain the brightness of the beam trace of said tube substantially constant, and means actuated by said second-named means for further controlling said grid to increase the brightness of said trace during said interval.

3. A controlcircuit for a cathode ray tube having beam deflecting electrodes and an intensity control grid, comprising a sweep generator for applying a varying sweep voltage of predetermined direction to said electrodes, an expander connected to said sweep generator for changing the rate of variation but not the direcvariation of said sweep voltage.

4. A control circuit for a-cathode ray tube having beam deflecting electrodes and an intensity control grid, comprising a sweep generator for applying a varying sweep voltage of predeteron to said electrodes, an expander connected to said sweep generator for changing direction of said being substantially greater than the change in rate-of variation of said sweep'voltage.

5. A sweep circuit for a cathode ray tube having beam deflecting electrodes comprising a condenser connected to said electrodes, alternately operative and inoperative means for charging to supply a constantly varying sweep voltage to said electrodes, and means for changing said resistance to modify said discharge rate during a predetermined interval of said discharge pecharged during positive port1ons ofsaid square wave and is isolated from said source during negative portions of said square wave; a pentode tube connected inpar'allel with said condenser,

whereby during said negative portions of said stant rate through said pentode, and means for modifying said constant rate, comprising means for applying a rate-modifying voltage to the control grid of said pentode during a predeter mined interval, the control grid :being returned to its original voltage during the remainder of each period following said interval.

7. A swee circuit for a cathode ray tube as in claim 6 further including means for controlling the phase relation between said rateinodifying voltage-and said square wave for adjusting the time relation of said interval.

8. In a control circuit for a cathode ray tube having beam deflecting means, sweep generator means for controlling said deflecting means ac sweep voltage REFERENCES CITED The following references are of record'in the file of this patent: V

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